CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating Activities:
Net income	$ 35,881	$ 27,606
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization expense	20,258	18,356
Deferred income taxes	13,693	15,408
Stock-based compensation and other	3,173	6,016
Changes in assets and liabilities	(80,453)	(49,428)
Net cash (used in) provided by operating activities	(7,448)	17,958
Investing Activities:
Capital expenditures	(19,833)	(31,740)
Purchase price adjustment	4,000	0
Net cash used in investing activities	(15,833)	(31,740)
Financing Activities:
Principal payments on long-term obligations	(3,750)	0
Net proceeds from issuances of common stock	3,786	846
Tax benefit of stock-based compensation	1,612	68
Net cash provided by financing activities	1,648	914
Net decrease in cash and cash equivalents	(21,633)	(12,868)
Cash and cash equivalents, beginning of period	232,324	259,219
Cash and cash equivalents, end of period	$ 210,691	$ 246,351